This invention relates to a brush seal for turbo-engines of the type having an engine rotor and stator with a bristle bundle held in sliding sealing contact with the rotor intermediate an upstream high pressure space and a downstream low pressure space.
Brush seals of the above-mentioned type (German Patent Document DE 39 07 614 A1) are used in turbo-engines, particularly gas turbine engines, in order to seal off spaces with respect to one another with as little leakage flux as possible on circumferential gaps which are acted upon fluidically by pressure in different manners, for example, between an engine casing and the rotor or an engine shaft. It must be possible in this case to compensate eccentric rotor or shaft positions relative to the casing resulting, for example, from unbalanced rotor masses by means of an elastic and movable following of bristles.
It is a significant disadvantage of the above-mentioned as well as of other known brush seals that, as a result of the shaft rotation, the bristles of the brush are subjected to a rotating turbulent flow which has a negative effect on the shape and the intended geometrical arrangement of the brush and therefore on the sealing effect. The turbulent flow has a particularly negative effect on the local position of those free ends of the bristles which project with respect to the ends of-guide webs in the direction of the rotor surface or shaft surface. A reliable, low-leakage primary sealing is therefore not ensured. The above-mentioned turbulent flow and its disadvantageous consequences can also not be excluded on the low-pressure side of the seal. In addition, the formation of individual and particularly pronounced types and geometries of turbulences may still be increased by special shaft-side surface geometries and attachments (screws, beads, steps).
It is an object of the invention to provide a brush seal of the initially mentioned type which, in view of a rotating turbulent flow or turbulence formation caused by the shaft ensures the maintaining of the shape and geometry of the bristles for the purpose of an optimal sealing.
According to the invention, this object is achieved by providing a brush assembly of the type having an engine rotor and an engine stator, comprising a bristle bundle, a bundle holder holding the bundle in sliding sealing contact with one of the engine rotor and engine stator intermediate an upstream high pressure space and a downstream low pressure space, and a turbulence reducer disposed upstream of at least some of the bristle bundle bristles.
By means of the invention, a rotating turbulent current which is generated by the rotating rotor in the space of the higher pressure in front of the device of the seal can largely be dissolved and can essentially be dissipated with respect to its original energy content. Thus, a significant portion of the turbulent flow of the fluid which is now already relatively calm flows off into the axial ring duct in front of the seal (bristle bundle) in which the flow rate of the fluid, such as air, is increased, with a simultaneously occurring pressure reduction in the axial ring duct relative to the higher pressure level which exists in the space or the annulus in front of the device. The axial ring duct represents an additional "calming path" for the fluid flowing out of the space of the higher pressure against the bristle bundle. A remaining portion of the rotating turbulent flow, for the purpose of the above-mentioned turbulence calming or resolving, flows off laterally into the device and flows essentially in the radial direction along the radially interior circumferential surface of the device into the axial ring gap.
According to certain preferred embodiments of the invention, the turbulence reducer is advantageously a shielding device which is a component of the bristle bundle or package. The shielding device effectively protects and stabilizes the bristle bundle with respect to a rotating turbulent flow. In this case, the bristles of a bristle bundle are guided along the respective larger portion of their longitudinal course between the axially spaced webs and are shielded with respect to the local pressure spaces. The axial gap, whose gap flank may in each case be formed by a shielding device, may be constructed of a smaller gap width and may be dimensioned to be essentially approximately 1/10 of the maximal width of the bristle bundle. This axial gap prevents a local forcing of the bristles between the two webs and ensures a required minimum play of the bristles in the circumferential and axial direction. In addition, by way of this axial gap, a circumferentially uniform fluid pressure distribution can be achieved on the respective shielding device and other bristle components of the bundle adjoining on the inside.
According to a variant of the invention, the shielding device may be formed of at least one layer or row of bristles of a relatively large bristle or thread thickness on the bristle bundle. The largest bristle thickness should be dimensioned such that, among other things, these thick bristles also ensure the required deformation elasticity for the purpose of an optimal sealing.
An increased overall stability with respect to a turbulent flow which may possibly also occur on the low-pressure side is obtained by providing at least one layer or row of bristles of a relatively large bristle or thread thicker on both the upstream and downstream sides.
The sealing effect and the overall stability of the bristle bundle can be increased if--in addition to the existing shielding devices--there is a construction of the bundle with a thread thickness or bristle thickness which changes in layers or rows.
Other preferred embodiments include a turbulence reducer in the form of a shielding device constructed as a wire netting. The wire netting can be formed of cross-soldered or mutually interwoven fine wires. By way of the meshes of the wire netting, for example, a rotating air swirl can be damped or largely neutralized. When this "shielding device" is arranged on the high-pressure and the low-pressure side, the bristles are axially held together in a manner of cage so that axial bristle deflections can also be limited, particularly on the brush end which projects laterally out of the webs. The wire netting has a ring-shaped construction and is held with play by means of a central bore with respect to the rotor or the shaft.
According to other preferred embodiments the turbulence reducer is separate from and spaced from the bristle bundle in an upstream high pressure space.
According to certain preferred embodiments the turbulence reducer is advantageously constructed as a porously ducted ring body.
In the case of preferred embodiments of the invention, the bristles of a bristle bundle are guided along the respective larger portion of their longitudinal course between axially spaced webs and are shielded with respect to the pressure spaces. The axial gap between the upstream web and the bristle bundle is constructed of a smaller gap width and may be dimensioned to be essentially approximately 1/10 of the maximal width of the bristle bundle. As mentioned above for the other embodiments where the turbulence reducer is part of or connected directly to the bristle bundle, this axial gap prevents a local forcing of the bristles between the two webs and ensures a required minimum play of the bristles in the circumferential and axial direction. In addition, by way of this axial gap, a circumferentially uniform fluid pressure distribution can be achieved on the upstream circumferential side of the bristle bundle.
According to preferred embodiments the turbulence reducer includes a metallic sponge whose porous structure is adapted to the dissipation of the turbulence as well as to the guiding of the fluid through the ring body in the direction of the axial ring duct. The sponge may be constructed of a metallic light construction material, such as a titanium aluminide of a globular cell structure. It may also be made in the manner of a hollow ball in several sintering steps from an intermetallic compound or its alloys. By means of the hollow-ball structure, the porosity or a corresponding duct arrangement can be taken into account during the manufacturing.
According to other preferred embodiments the turbulence reducer is represented by a ring body constructed in the manner of a honeycomb, in which case radial or axial or combined axial, radial ducts which are locally connected with one another fluidically are constructed along the honeycomb structure or integrated in it. According to certain embodiments, the axial ducts on the ends facing away from the high-pressure side lead into a circumferential gap which is connected with the axial ring duct.
Particularly while using another metal sponge for the turbulence reducer, an increased sealing effect is achieved within the scope of a multistep pressure seal according to certain preferred embodiments. Possibly still existing residual turbulences in the flow downstream of the first seal can in this manner be completely eliminated in front of the second seal.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.